This section provides background information related to the present disclosure which is not necessarily prior art.
A clutch arrangement may serve in a motor vehicle with all-wheel drive, for example, in dependence on a difference in speed between a permanently driven primary axle and a driven secondary axle that may be switched in to transmit the driving torque of a drive unit to the secondary axle. In other applications, a clutch arrangement may serve as a replacement of an axle differential for the transmission of a driving torque to a half-shaft of an axle as a block for a longitudinal differential of an all-wheel driven vehicle or as a block for an axle differential.
Such a clutch arrangement has an input element and an output element (e.g., an input shaft and an output shaft) which may be rotated relative to one another. The clutch arrangement typically has a friction clutch by which the input element and the output element may be operably effectively coupled to one another. The friction clutch is effective in dependence on a hydraulic pressure that prevails in a pressure space of the clutch arrangement. This pressure may be generated by a pump that is responsive to a speed difference between the input element and the output element. The pump may, for example, be a so-called gerotor pump or a P-rotor pump.
When a speed difference is present between the input element and the output element, the pump is driven such that hydraulic fluid is conveyed into the pressure space of the clutch arrangement to actuate the friction clutch. A friction locking coupling is hereby effected between the input element and the output element of the clutch arrangement, which in turn contributes to a reduction in the speed difference between the input element and the output element and, therefore, to a reduced pump power.
It is desirable for some applications to be able to control this generally self-regulating mechanism. The clutch arrangement should therefore be able to be deactivated (i.e., the transmission of a torque from the input element to the output element should be able to be interrupted) in dependence on specific driving states of the vehicle or on the detection of predetermined driving state parameters. It should, however, in turn be avoided that the clutch arrangement is deactivated as long as a significant torque is still being transmitted from the input element to the output element. The deactivation of the clutch arrangement would otherwise be associated with a noticeable load pressure and there would even be the worry of an impairment of the driving stability under certain circumstances. It is admittedly generally possible to detect the instantaneously transmitted torque by suitable sensors to preclude a deactivation of the clutch arrangement as long as a significant torque is being transmitted. The detection of the instantaneously actually transmitted torque is, however, undesirably complex and, therefore, expensive.
The use of proportional valves is also known to be able to actively control the torque transmission while avoiding an undesired load reversal. The use of such proportional valves is, however, likewise undesirably complex.